(1) Field of the Invention
The present invention relates to very sensitive optical devices for detecting or measuring many physical phenomena using the techniques of optical interferometry. More particularly, this invention relates to a system for sensing a given physical quantity to be measured by applying optical fibers for remote measurement, further permitting the use of multimode optical fibers with all kinds of light sources including white light.
(2) Description of the Prior Art
All physical phenomena are generally measured by sensing one of the physical effects they produce. Consequently, there are a large variety of sensing devices. Very often, however, these devices have not been sufficiently sensitive, safe or simple. With the availability of optical fibers, it became desirable to perform measurements optically to permit simplified remote operation thereby improving sensitivity while reducing size and weight. Recently, a number of optically operated sensing devices using single mode fibers have been disclosed. Single mode operation, however, encounters many implementation difficulties, such as the requirement for a single mode light source such as a laser, the need to maintain light beam polarization, and focusing difficulties and maintenance of focus problems.
The Acousto-Optic Transducer, described in my U.S. Pat. No. 4,188,096 and my Wide-Area Optical Hydrophone, U.S. patent application Ser. No. 277,297, filed, 6/25/81, now U.S. Pat. No. 4,422,167, are optically operated sensing devices for detecting acoustic pressure. They operate free from the above stated difficulties using multimode optical fibers and white light. In these devices the optical fibers are only used to transmit light to and from the sensor while a special sensing element directly modulates the light beam. The light beam is modulated by varying the optical pathlength in one arm of an interferometer. In my Acousto-Optic Transducer, the actual beam length was varied by moving mirrors, while in my Wide-Area Optical Hydrophone, the index of refraction of the medium in which the light beam propagates was varied. Demodulation was performed with an interferometer, where the modulated signal beam was compared with the nonmodulated reference beam.
What is generally needed are sensing devices which can measure a wide range of physical phenomena using the principle of operation of the Acousto-Optic Transducer and the Wide-Area Optical Hydrophone. In addition to inherent high sensitivity, such devices would offer simplicity, low cost, freedom from electro-magnetic interference and safe operation.